1. Field of the Invention
The present invention relates to the class of devices for performing electrophotography, and more particularly, to the class of devices known as fixing units which are used in electrophotographic devices.
2. Description of the Related Art
Electrophotographic devices are widely used in applications such as photocopying, laser printing and facsimile printing. An electrophotographic image forming apparatus is composed of a sheet feeding unit for feeding recording sheets one by one, an image forming unit for forming an image on the fed sheet with a toner, a fixing unit for fixing the toner on the sheet, and a sheet discharging unit for discharging the sheet with the toner fixed thereon. Further, the fixing unit is composed of a heating roller for melting toner particles covering a latent image on the sheet and a pressure roller for pressing the melted toner particles on the sheet, rotating in contact with the heating roller. It is often necessary for the user to access the fixing unit, especially in the case of a jammed sheet.
In one example of a fixing unit, a guide door is positioned where the sheet exits the rollers to help guide the sheet from the rollers. The guide door is hinged to open to allow access to the rollers in the event of a jammed sheet. The hinge axis of the guide door is parallel to the axis of the heating and pressure rollers, and the guide door moves vertically relative to the rollers and the frame. Upon opening the guide door around its hinge axis, there is not enough space for the user to have full access to the rollers. Therefore, it might be difficult for the user to completely remove the pieces of the jammed sheet.
This general arrangement of a guide door opening vertically relative to the rollers is illustrated in fixing devices seen, for example, in the following U.S. Patents. U.S. Pat. No. 4,598,990, is to Kusumoto et al., entitled Toner Image Fixing Device, describes a toner fixing device which is hinged on a shaft member to lift the supporting frame holding the heating to fixing roller. In this device an entire portion of the frame must be lifted to access the rollers as the hinge axis is parallel to the rollers. U.S. Pat. No. 4,756,687, to Cabrera et al., entitled Roller Fuser Jam Clearance Mechanism, describes a fixing unit with a handle for moving a sheet guide from the rollers. All of the movement of the parts occurs along axes parallel to the rollers, and the rollers are not fully accessible when open.
U.S. Pat. No. 4,806,970, to Nakatomi et al., entitled Recording Apparatus Having An Accessible Housing, describes a laser printer having a fixing unit, where the entire upper cover of the printer, containing many components, is hinged parallel to the rollers and must be lifted to access the interior. This patent also shows an upper frame of the fixing unit, hinged along an axis parallel to the rollers, which is rotated up to access the fixing unit. Even when the upper frame of the fixing unit is rotated up, it still does not provide full access to the rollers. U.S. Pat. No. 4,965,640, to Watarai et al., entitled Image Forming Apparatus Including Detachable Toner Fixing Unit, describes a fixing unit in which the entire upper frame, hinged parallel to the rollers, is lifted to access the fixing unit. Opening the frame loosens the contact between the rollers, but actual access to the rollers is limited. U.S. Pat. No. 5,045,887, to Nakamura, Fixing Device With A Selectively Movable Cover, describes a fixing device with a cover which rotates vertically to separate the heating and pressure rollers. The cover is hinged parallel to the rollers and does not open so as to give full access to the rollers. U.S. Pat. No. 5,179,415, to Ikematsu et al., entitled Electro-Photographic Printing Apparatus Comprising A Toner Fixing Unit, describes a fixing unit in which a sub-frame containing the pressure roller rotates away from the frame containing the heating roller to allow removal of jammed sheets. The subframe has a hinge axis parallel to the axis of the rollers. This arrangement does not allow access to the rollers while the rollers are together, however.
Based on my observation of the art, then, I have discovered that what is needed is a guide door for a fixing unit which allows full access to the rollers of the unit, especially to remove jammed sheets. Specifically, what is needed is a guide door which does not open vertically with respect to the fixing unit, and which is easy to open and close.